PUNTA GORDA, Fla. — In what has become an all-too-familiar drill, Floridians boarded up windows, gassed up their cars and bought storm supplies Wednesday. But this time they were looking at one of the most intense hurricanes ever recorded in the Atlantic.

Hurricane Wilma exploded briefly into a Category 5 monster with winds of 175 mph before weakening to a Category 4 Wednesday night. Forecasters warned it could smash into southwestern Florida on Saturday with towering waves, and then work its way up the East Coast with devastating effect.

“I don’t think I want to live in Florida,” said Betty Bartelson, a Pennsylvania tourist visiting Marco Island. She planned to flee across the state to Fort Lauderdale.

Like Hurricanes Katrina and Rita earlier this season, Wilma was expected to weaken before coming ashore. But after seeing what those storms did — and after four storms hit Florida in quick succession last year — many people were taking no chances.

Officials began clearing tens of thousands of people out of the low-lying Florida Keys.

“We had well over a 1,000 lives lost in Katrina. If Wilma, you know, comes into the U.S., to the Florida coast as a Category 3 or 4 hurricane, that potential for large loss of life is with us,” National Hurricane Center Director Max Mayfield said.

At one point, Wilma was the most intense hurricane recorded in the Atlantic as measured by its pressure. Early Wednesday, the storm’s pressure dropped to 882 millibars, the lowest reading ever in an Atlantic-basin hurricane. Typically, the lower the pressure, the faster air rushes into a storm.

By evening, Wilma had weakened, with its winds dropping to 155 mph, and its pressure rising to 894 millibars as it wobbled in the northwestern Caribbean. Forecasters warned it could re-intensify Thursday.

The previous strongest Atlantic storm on record, based on pressure readings, had been Hurricane Gilbert in 1988, which registered 888 millibars.

The hurricane center was predicting that the storm would move into the Gulf of Mexico and then swerve east, toward southwestern Florida.

Mayfield said Wilma might not reach the Florida Keys until Saturday, possibly toward the evening. It had earlier been expected to reach the Florida mainland Saturday.

Wilma was on a path that could threaten the areas hit last year by Hurricane Charley. Some houses and businesses in the area are still boarded up because of that storm.

The White House promised to stay on top of the situation, hoping to avoid a repeat of the slow initial response to Katrina. The Federal Emergency Management Agency was positioning emergency materials in Jacksonville, Lakeland and Homestead.

Gov. Jeb Bush said the state had ample supplies of food, water and ice ready for hard-hit areas.

Sean Mayo was filling up his sport utility vehicle’s 26-gallon tank and a five-gallon gas can in Marco Island. “We don’t know if there will be any shortages. I need to make sure I got enough gas to get to Lauderdale and back,” he said.

Although Wilma was approaching from the west, forecasters warned that Atlantic Coast cities such as Miami, Fort Lauderdale and West Palm Beach could be hit by winds nearly as strong.

At 11 p.m. EDT, Wilma was centered about 235 miles southeast of Cozumel, Mexico, and 474 miles south-southwest of Key West. It was moving west northwest at about 8 mph, forecasters said.

Mayfield said the Keys could be hit by storm surge up to 25 feet and battering waves ever higher than that.

“I just don’t see how the Florida Keys will get out of this without having a major impact,” he said.

Authorities told visitors to leave the Keys on Wednesday and planned to order residents to get out on Thursday. The Keys were evacuated for Hurricanes Dennis and Rita earlier this year and four times last year.

“It is tough on the nerves,” said Leon Dermer, owner of Happy Feather Gift Shop in Key Largo. He said every evacuation costs him about $10,000.